RICHARDS AND PARKER. — BARIC SULPHATE. 69 



sure accuracy. It is convenient to state first the experiments which 

 determined the true strength of the standard acid, although these 

 were made at a later stage of the work, when more experience had 

 been gained. 



In order to secure a standard of comparison which should be wholly 

 different from the method under investigation, the strength of the sul- 

 phuric acid was determined alkalimetrically. Weighed portions of 

 the solutions were almost neutralized with weighed portions of very 

 pure gently ignited sodic carbonate, which had been crystallized ten 

 times successively in platinum vessels. This neutralization was con- 

 ducted in dilute solutions, so that there might be no loss of substance 

 from the active effervescence. The dilute solutions were then evapo- 

 rated to small bulk in platinum dishes, and the small excess of sodic 

 carbonate required to complete the neutralization was added in dilute 

 standard solution, methyl-orange being used as the indicator. This 

 method, which may easily be made to give results accurate to within 

 the hundredth of one per cent (one part in ten thousand) was devised 

 for use in the investigation upon copper. 



(1.) 18.6132 grams of the sulphuric acid solution required 0.62o4 

 gram of dry sodic carbonate and 12.30 cubic centimeters of sodic 

 carbonate solution (1 c.c.= 0.001793 gram of the salt), or in all 

 0.6475 gram for its neutralization. 



(2.) 20.3966 grams of the acid solution required 0.6761 gram of 

 dry sodic carbonate and 18.50 cubic centimeters of solution — in all 

 0.7092 gram of salt — for its neutralization. 



The results of these analyses are precisely identical, each showing 

 the acid solution to contain 3.214 per cent of HoSO^. It was impor- 

 tant now to determine whether under the most favorable circum- 

 stances similar results might be obtained from the usual method of 

 precipitation. All the precautions necessary to make the occlusion of 

 baric chloride as small as possible, which are discussed later, were 

 practised, and a very slight excess only of baric chloride was used. 

 The precipitates after long standing were washed with as little freshly 

 distilled water as was necessary to free them from every trace of acid, 

 and the filtrates (each measuring about a hundred and thirty cubic 

 centimeters) were evaporated to very small bulk in platinum dishes, 

 allowed to stand, and filtered through tiny filters in order to collect 

 the baric sulphate which had been dissolved by the acid solution. 

 Finally, the baric sulphate was all fused with pure sodic carbonate ; 

 and the aqueous extract was acidified with nitric acid. The chlorine 

 was now precipitated as argentic chloride, which was collected and 

 weighed upon a Gooch crucible. 



